1. Field of the Invention
The present invention relates to a carbon monoxide sensor for detecting carbon monoxide in a gas, especially its concentration in the gas. The sensor of the present invention decreases an error caused by oxygen in a gas.
2. Description of Related Art
Carbon monoxide is a colorless, odorless, and toxic gas. A carbon monoxide sensor can be used industrially and domestically.
To detect a carbon monoxide concentration in an exhaust gas from an internal combustion engine is important since the concentration affects an air-to-fuel ratio of the internal combustion engine thereby affecting response thereof.
Japanese Patent Application hid-Open No. 2-91443 discloses a carbon monoxide sensor having a zirconia substrate, a pair of platinum electrodes, and another pair of gold electrodes. The sensor determines a carbon monoxide concentration based on a difference between a potential difference of the platinum electrodes and a potential difference of the gold electrodes. However, the sensor is influenced by a partial pressure of oxygen in a gas. Therefore, even though a carbon monoxide concentration is constant, the sensor may give a varying value of the carbon monoxide concentration depending on the partial pressure of oxygen.